Transformer Turns Ratio Calculator

The Transformer Turns Ratio Calculator determines the voltage transformation ratio, secondary voltage, secondary current, and impedance transformation ratio from the turns count and primary electrical quantities. The turns ratio is the most fundamental parameter of any transformer, governing all voltage, current, and impedance transformations between windings.

The turns ratio a = N₁/N₂ directly gives the voltage transformation: V₂ = V₁/a. For a step-down transformer with a = 10, a 1000V primary yields a 100V secondary. Current transforms inversely: I₂ = I₁ × a, preserving apparent power (V₁I₁ = V₂I₂ in an ideal transformer).

The impedance transformation ratio is a² — arguably the most important property for circuit analysis. An impedance Z_L connected to the secondary appears as Z_L × a² when referred to the primary. This impedance reflection technique is used extensively in audio transformers (matching amplifier output impedance to speaker impedance), RF transformers, and power system analysis.

In power engineering, the turns ratio is used for current transformer (CT) design — a CT with 600:5 ratio steps down line current by a factor of 120, allowing 5A-range instruments to measure high primary currents safely. Potential transformers (PTs/VTs) similarly step down high voltages for metering, typically to 110V or 120V secondary.

Measuring turns ratio in the field uses a turns ratio tester (TTR) that applies a low AC voltage to one winding and measures the other. Deviations from nameplate ratio indicate shorted turns, open circuits, or winding damage. Typical acceptance criteria for distribution transformers require turns ratio within 0.5% of nameplate value.